Pristine processing, where high purity and contamination control are extremely important, is a familiar concept for pharmaceutical production and microelectronics fabrication. Increasingly, it is also an issue for the manufacture of agricultural and fine chemicals, and in environmentally sensitive processes. Therefore a proper valve selection must be considered. Compared with other applications where valves are used, clean processes typically have three major distinctions: different types of valve are used, more valves are used, more valves are actuated and automatically controlled. In contamination-sensitive processes, the first step is to select valves that do not harbor trace amounts of contaminants, and are easy to clean. Manufacturers with valves that meet sanitary standards may submit them to the 3A Symbol Council, which will then decide whether to authorize the use of the registered 3A symbol on the valve. The author of this paper investigated diaphragm valves, check valves, ball valves, plug valves and some varieties. Gate valves and most designs of check valves have contamination problems. The 3A standard for check valves accepts a spring-loaded check and an angled-ball check. Diaphragm valves are a good choice, when conditions and budgets allow. However, pinch valves, for which there is no 3A standard, also offer possibilities. Full-port plug valves and ball valves are vera reasonable compromises as a block valves in most high-purity processes, and a V-ball valve is a good choice as a control valve. Butterfly valves, for which there is also no 3A standard, may make sense in very large lines. They pose problems, though, because of their corners, where contaminants can collect and adhere. Finally, gate valves should never be used. Generally, clean processes require more valves in the piping systems than do other chemical processes. Ideally, the pipe run should be short and its valve conveniently located. Aim to have both the upstream leg and downstream leg less than two diameters long. A typical feature of ultrapure processing is its elaborate cleaning sequence. Systems can be operated automatically or manually, but the risks associated with manual systems are greater because of mistakes by the operator. The 3A mark is a good plasce to begin looking for valves, but it is not the final word. The 3A mark is not a universal guarantee of suitability.


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    Title :

    Selecting clean valves. The 3A mark does not mean that a particular valve is suitable for all high-purity processes


    Additional title:

    Ventilauswahl für hochreine Prozesse


    Contributors:
    Schmidt, M. (author)

    Published in:

    Publication date :

    2001


    Size :

    4 Seiten, 5 Bilder



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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